Siamese Fighting Fish, a tropical freshwater fish of Thailand (formerly Siam). It is one of a group of tropical fish called bettas. The Siamese fighting fish is yellowish brown and patterned with bright greens, blues, and reds. It has a rounded tail and short fins. The adult is about 2 ½ inches (6.4 cm) long.

The Siamese fighting fishThe Siamese fighting fish is yellow-brown and patterned in bright green, blue, and red.

The male of the species is the fighter. When two males meet they attack each other, nip each other's fins and gills, and often lock jaws. In Thailand large sums of money are bet at fish fights. A contest ends when one of the two fish flees.

Although it obtains oxygen from the water, the Siamese fighting fish also occasionally surfaces to gulp air. Before mating, the male builds a “bubble nest” by blowing saliva-coated bubbles to the surface of the water, where the bubbles form a frothy mass. The male places the fertilized eggs in the nest and guards the nest for about two days until the eggs hatch. The nest usually contains from 100 to 500 eggs.

The Siamese fighting fish is Betta splendens of the family Belontiidae.